The Right Layer

Wednesday, July 25, 2012

Layer and Let It Be
Summer is for layering, a form of propagation that relies heavily on time and technique to be successful. When it comes to layering, there is no substitute for practice and many plants are at just the right growth stage for it now. I’m layering figs, both edible and ornamental, but they are just examples of what is possible now, at the height of the growing season. Gather a few needed items and get busy!
Layering works because of one universal principle: wounding triggers biochemical survival mechanisms. You can think of it as the plant version of fight or flight, the adrenaline response in threatened mammals. We’ve all heard of people who are able to lift automobiles off of their loved ones, and soldiers who continue to defend their comrades despite their wounds. My only brush with such power came during a move when a refrigerator dolly slipped going upstairs and my husband was trapped underneath the appliance. Without thinking, I squeezed my shoulder into the small space available and lifted more weight than I ever imagined possible so he could roll out from underneath. Thanks to adrenaline, we managed to prop the fridge up on the porch rail, retrieve the dolly and finish moving in. I didn’t even get a bruise!
Auxin hormones control many aspects of plant growth and were the first plant hormones ever discovered. Their presence and levels throughout a plant will stimulate or repress depending on complex triggers. Cell growth and division, the way a particular plant organizes itself into leaves, buds, etc., and phenomena like apical cell dominance depend on auxin movement to occur. APC varies which explains why some plants put on new growth only at the tips of branches and others sprout at every node. It also explains why trees like cedars will usually die if their tops are cut out. Their apical dominance is so intense that removing the growing point stops them cold. Other plants can continue to grow without their central leader but will grow sideways or send branches weeping downward instead of up. For example, to maintain desirable cascading habits in plants like weeping mulberry you are advised to clip off any shoots that grow straight up. That tip is not just to keep them from looking like impish spiked hair – it continues the suppression of apical dominance. All of this may seem irrelevant, but it is not. Both the techniques and choice of plant parts to layer depend on it.
The best air layers are made on healthy plant stems at least 1 inch in diameter and held stiffly above ground. Woody plants like my edible fig trees with mature, inflexible stems are good candidates as are plants that grow from thickened canes such as corn plant and Janet Craig Draceanas. I must confess there is a sad JC struggling on a porch in my neighborhood that could be layered easily and recover its previous glory at the same time. Its 8 inch pot is inadequate for the 7 foot tall specimen with 2 fat stems and huge crowns of sadly weeping, sunburned leaves. There are clumps of leaves at the top of each stem and more a few feet lower down the cane. If I could make air layers along the stems below the top growth and above the lower, the 2 babies would be new plants and with some basic TLC, the mother could recover. Layering depends on healthy tissue and enough auxin to make the classic wound reaction, so time is of the essence here. I’m hoping to see JC out by the trash pile so I can save it, but not if too much time passes and the plant dehydrates completely.
To make an air layer, gather these items: sharp knife, ½ gallon of water in a small bucket, long-fibered sphagnum moss, 1 square foot of clear plastic, 2 twist ties, 1 toothpick, and Hormex Liquid Concentrate. Select a place below the top growth on the bare plant stem that is about 6 inches long. Add 1 teaspoon of HLC to the water and soak 2 handfuls of moss and the toothpick in the bucket for 15 minutes. Make a half inch slit across the stem and wedge it open with a piece of the soaked toothpick. By forcing open the slit, you hinder the natural auxin process that would regenerate the wounded vascular system and by soaking the toothpick in HLC you redirect the biochemistry in the wound in favor of root development. Squeeze out most of the excess water and press the moss into and around the wound to form a football shaped clump that extends 3 inches above and below the slit. Wrap plastic around the moss mass and secure it above and below with twist ties. Now, make another – remember, this is all about practicing to master the techniques – and make a note on your calendar to check on the air layer in about one month. Depending on the plant in question, you may be able to see white roots through the plastic as they grow in the moss. Smile, but wait until you see numerous roots before cutting the clone from its mother. Might be a month, might be 3, but time is on your side so use it.
Next week: Part 2: how to make ground layers that will really grow.